WASHINGTON - The fate of the Medicare prescription drug bill rests with 100 senators after the measure narrowly passed the House, which endured a dusk-to-dawn debate capped by the longest roll call vote in the chamber's history.

Already there was a pledge to try to stall the bill.

President Bush, eager to sign it and promote it on the campaign trail, praised the 220-215 passage in the Republican-controlled House.

''We're on the verge of success'' of modernizing and strengthening Medicare, Bush said Saturday in a radio address that aired hours after the vote.

In the Senate, which began an expected three days of debate soon after Bush spoke, there were conflicting signs about whether the partisan struggle in the House would be repeated in the Senate.

''I think you'll see an entirely different atmosphere in the Senate,'' said Sen. John Breaux, D-La., one of the architects of the compromise.

Senate Democratic leader Tom Daschle of South Dakota said Friday he would oppose a filibuster to delay a vote on the legislation, even though Daschle said he plans to vote against the bill.

But the extraordinary House vote, which GOP leaders held open for nearly three hours while they pursued Republican holdouts, brought the promise of a filibuster from Sen. Edward M. Kennedy, D-Mass.

''Give this bill a fair vote in the House and I'll drop my filibuster in the Senate,'' Kennedy said in a statement.

Senate Majority Leader Bill Frist, R-Tenn., was prepared to seek a vote Monday to end a filibuster, his spokesman said.

The legislation's backers would need 60 votes to close off debate and hold a final vote on the Medicare legislation, which would give 40 million older and disabled Americans a prescription drug benefit and a new option for private health care coverage.

Republican plans to pass the bill and send it to the president before before Thanksgiving were nearly thrown into disarray by the House vote.

The outcome remained unsettled until just before 6 a.m. Saturday, when Repub-licans finally overcame a rebellion by conservatives in their own ranks and the overwhelming opposition of Democrats.

Roll call votes in the House customarily last 15 minutes to allow lawmakers ample time to reach the chamber.

''We won it fair and square and they stole it by hook and crook,'' countered House Democratic leader Nancy Pelosi of California.

Dozens of lawmakers, participants and spectators both, waited out the drama of the middle-of-the-night roll call.

Hastert, his lieutenants and Health and Human Services Department Secretary Tommy Thompson shuttled from one GOP holdout to another seeking enough votes to prevail. The president lobbied about a dozen lawmakers by phone from the White House late Friday and early Saturday.

Frist said awoke twice in the middle of the night to check the progress on C-SPAN. ''I got up at 5, saw the vote on the screen and said, 'Oh my goodness,''' he said.

The vote was stuck at 216 to 218 for over an hour, the bill seemingly on its way to defeat before a flurry of last-minute switches.

''I did not want to vote for this bill,'' said Rep. Butch Otter, R-Idaho. But he did, as did a handful of late GOP converts.

He said afterward he became convinced that if the measure were defeated, another one would come back to the House floor even less to his liking.

The bill drew the support of 204 Republicans and 16 Demo-crats, many of whom waited until the bill appeared on the verge of passage in the final moments of the roll call before swinging behind it. Voting no were 189 Democrats, 25 Repub-licans and 1 independent.

As written, the legislation would virtually remake Medi-care.

For the first time, the legislation would also require those older Americans with annual incomes over $80,000 to pay higher premiums under Medicare Part B, which covers services outside the hospital.

Additionally, it would establish new tax-preferred health accounts, open to individuals with high-deductible insurance policies.

The tax provision and the requirement for higher premiums were part of an effort to appeal to conservatives who favor transforming Medicare and restraining its cost, yet find creation of the new prescription drug benefit distasteful.